Method for determining partial pressure of a gaseous constituent and regulator of breathing mask for aircraft occupant

ABSTRACT

A method for determining a characteristic such as partial pressure or percentage of a gaseous constituent in a first gas mixture flow ( 32 ) in a flow chamber ( 30 ) where flows alternatively said first gas mixture flow ( 32 ) and a second gas mixture flow ( 34 ) comprising the following steps: a) introducing the first gas mixture flow ( 32 ) into a sensing chamber ( 40 ) when the first gas mixture flow ( 32 ) flows in the flow chamber ( 30 ), b) preventing introduction of gas from the flow chamber ( 30 ) into the sensing chamber ( 40 ) at least when the second gas mixture flow ( 34 ) flows in the flow chamber ( 30 ), c) sensing said characteristic of the first gas mixture flow ( 32 ) in the sensing chamber ( 40 ).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the United States national phase of InternationalApplication No. PCT/IB2011/000781 filed on Feb. 28, 2011 and publishedin English on Sep. 1, 2011 as International Publication No.WO2011/104635, which application claims priority to U.S. ProvisionalApplication No. 61/308,476 filed on Feb. 26, 2010, the contents of bothof which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a method for determining acharacteristic such as partial pressure or percentage of a gaseousconstituent and a regulator of breathing mask for aircraft occupant. Thegaseous constituent is in particular oxygen or carbon dioxide.

BACKGROUND OF THE INVENTION

The partial pressure or percentage of oxygen (and carbon dioxide) areparticularly useful in order to satisfy the needs of the user whilereducing the consumption in pure oxygen (provided by an oxygen cylinder,a chemical generator or a liquid oxygen converter) or gas highlyenriched in oxygen provided in particular by an on-board oxygengenerator system (OBOGS).

But, when two gases having different mixtures successively flow inopposite directions in a chamber, the measurement of a characteristic ofa gaseous constituent in the first gas mixture flow is disturbed by thesecond gas mixture. The invention aims at reducing this problem.

SUMMARY OF THE INVENTION

For this purpose the invention provides a method for determining acharacteristic such as partial pressure or percentage of a gaseousconstituent in a first gas mixture flow in a flow chamber where flowsalternatively said first gas mixture flow and a second gas mixture flowin opposite directions comprising the following steps:

a) introducing the first gas mixture flow into a sensing chamber whenthe first gas mixture flow flows in the flow chamber,

b) preventing introduction of gas from the flow chamber into the sensingchamber at least when the second gas mixture flow flows in the flowchamber,

c) sensing said characteristic of the first gas mixture flow in thesensing chamber.

According to another feature in accordance with the invention,preferably the method further has the following steps:

-   -   providing a user with a breathing mask for aircraft occupant        including a demand regulator,    -   generating a respiratory gas flow by breathing in of the user        into the flow chamber, and    -   generating an exhalation gas flow by breathing out of the user        into the flow chamber, one amongst the respiratory gas flow and        the exhalation gas flow being the first gas mixture flow and the        other being the second gas mixture flow.

According to a supplementary feature in accordance with the invention,preferably the method further has the following steps:

-   -   splitting the flow chamber in a respiratory chamber and sensing        chamber,    -   inserting an isolation valve between the sensing chamber and the        respiratory chamber, in order to prevent introduction of the        second gas mixture flow into the sensing chamber,    -   generating the first gas mixture flow into the respiratory        chamber, by breathing of the user into the respiratory chamber.

According to a supplementary feature in accordance with the invention,preferably the method further comprising feeding the respiratory chamberwith the first gas mixture flow through the sensing chamber and theisolation valve.

According to an alternative feature in accordance with the invention,preferably the method comprising feeding sensing chamber with the firstgas mixture flow through the respiratory chamber and the isolationvalve.

According to another feature in accordance with the invention,preferably the method further comprises introducing the first gasmixture flow into the sensing chamber from the flow chamber during stepa).

According to a supplementary feature in accordance with the invention,preferably the method further comprises:

d) detecting the occurrence of the first gas mixture flow in the flowchamber,

-   -   during step a), putting the sensing chamber in flow        communication with the flow chamber when the occurrence of the        first gas mixture flow in the flow chamber is detected.

According to another supplementary feature in accordance with theinvention, preferably the method further comprises preventingcommunication between the flow chamber and the sensing chamber when theoccurrence of the first gas mixture flow in the flow chamber is notdetected.

According to another feature in accordance with the invention,preferably the method further comprises:

-   -   placing a solid ionic conductor of a pump electrochemical cell        interposed between the flow chamber and the sensing chamber, and    -   during step a), pumping said gas constituent from the flow        chamber into the sensing chamber through the solid ionic        conductor.

Otherwise, the invention provides a method for protecting aircraftoccupant comprising the steps of:

a) providing a user with a breathing mask for aircraft occupant,

b) providing a respiratory gas including a mixture of breathable gas anddilution gas to the user,

c) sensing partial pressure or percentage of oxygen or carbon dioxide inexhalation gas flow generated by the user,

d) adjusting the rate of oxygen or breathable gas in the respiratoryflow in accordance with the partial pressure or percentage of oxygen orcarbon dioxide.

It appears that the partial pressure or percentage of oxygen or carbondioxide in exhalation gas flow is an efficient indication concerning theoxygen need of user. Therefore, the consumption in oxygen can beaccurately adjusted.

The invention also provides a breathing mask for aircraft occupantincluding a demand regulator, said regulator comprising:

-   -   a breathable gas supply line to be connected to a source of        breathable gas and supplying a flow chamber with breathable gas,    -   a dilution gas supply line to be connected to a source of        dilution gas and supplying the flow chamber with dilution gas,    -   a dilution adjusting device adjusting the rate of dilution gas        in the respiratory gas supplied to the flow chamber, the        dilution adjusting device comprising a dilution valve and a        control device controlling the dilution valve in accordance with        a dilution signal generated by the gas sensor in function of the        partial pressure or percentage of oxygen or carbon dioxide in        exhalation gas.

In advantageous embodiments, the breathing assembly preferably furtherhas one or more of the following features:

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the present invention will appear inthe following detailed description, with reference to the appendeddrawings in which:

FIG. 1 shows a breathing mask comprising a flow chamber,

FIG. 2 schematically represents a first flow and a second flow in theflow chamber of the breathing mask, according to a sensing device notwithin the scope of the invention,

FIG. 3 represents variations of the first flow in the flow chamberduring the time,

FIG. 4 represents variations of the second flow in the flow chamberduring the time,

FIG. 5 represents measurements provided by gas sensors placed in theflow chamber,

FIG. 6 represents a first embodiment of a sensing device in accordancewith the invention,

FIG. 7 represents a second embodiment of a sensing device in accordancewith the invention,

FIG. 8 represents a third embodiment of a sensing device in accordancewith the invention,

FIG. 9 represents a fourth embodiment of a sensing device in accordancewith the invention,

FIG. 10 represents a step of a method according to the invention usingthe sensing device of the fourth embodiment,

FIG. 11 is a flowchart representing different steps according to theinvention,

FIG. 12 represents a method according to the invention,

FIG. 13 represents a variation of the method represented in FIG. 12.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 discloses main functions of a breathing mask 4 for occupant of anaircraft, in particular for pilot disposed in a cabin 10 of an aircraft.

The breathing mask 4 comprises a demand regulator 1 and an oronasal facepiece 3 fixed to a tubular connecting portion 5 of the regulator 1. Whena user 7 dons the breathing mask 4, the oronasal face piece 3 is put tothe skin of the user face 7 and delimits a respiratory chamber 9.

The demand regulator 1 has a casing 2 including a breathable gas supplyline 12, a dilution gas supply line 14 and a respiratory gas supply line16. The respiratory gas supply line 16 has a downstream end in fluidcommunication with the respiratory chamber 9.

The breathable gas supply line 12 is supplied at its upstream end withpressurized oxygen by a source of breathable gas 8 through a feedingduct 6. In the embodiment shown, the pressurized source of breathablegas 8 is a cylinder containing pressurized oxygen. The breathable gassupply line 12 supplies the respiratory chamber 9 with breathable gasthrough the respiratory gas supply line 16, the downstream end of thebreathable gas supply line 12 being directly in fluid communication withthe upstream end of the respiratory gas supply line 16.

The dilution gas supply line 14 is in communication by its upstream endwith a source of dilution gas. In the illustrated embodiment, thedilution gas is air and the source of dilution gas is the cabin 10 ofthe aircraft. The dilution gas supply line 14 supplies the respiratorychamber 9 with dilution gas through the respiratory gas supply line 16,the downstream end of the dilution gas supply line 14 being directly influid communication with the upstream end of the respiratory gas supplyline 16. So, in the embodiment illustrated, the breathable gas and thedilution gas are mixed in the respiratory gas supply line 16 of thecasing 2, i.e. before supplying the respiratory chamber 9 through thetubular connecting portion 5. Therefore a flow 62 of respiratory gasflows in the respiratory gas supply line 16 and the respiratory chamber9, the respiratory gas including breathable gas and dilution gas mixed.

The regulator 1 further comprises an exhaust line 18 and an exhaustvalve 20. The exhaust valve 20 is disposed between the downstream end ofthe exhaust line 18 and the cabin 10 (ambient air). The upstream end ofthe exhaust line 18 is in communication with the respiratory chamber 9of the oronasal face piece 3 through the tubular connecting portion 5and receives a flow 64 of gas exhaled by the user. Concerning theexhaust of the exhalation gas flow 64, the exhaust valve 20 functions asa check valve which opens under the pressure of the exhalation gas flow64 and closes for preventing air of the cabin 10 from entering into theflow chamber 30.

The user 7 breathes in and breathes out in the respiratory chamber 9.The exhalation line 18 is in communication directly or through therespiratory chamber 9 with the respiratory gas supply line 16.Therefore, the gas supply line 16, the respiratory chamber 9 and theexhalation line 18 define a flow chamber 30 without separation.

The demand regulator 1 further has a pressure adjusting device 22 and adilution adjusting device 24.

The pressure adjusting device 22 adjusts the pressure in the flowchamber 30 and in particular in the respiratory chamber 9. In theembodiment illustrated, the pressure adjusting device 22 comprises inparticular a main valve disposed between the feeding duct 6 and therespiratory gas supply line 16.

The dilution adjusting device 24 adjusts the rate of oxygen in therespiratory gas flow 62. In the embodiment illustrated, the dilutionadjusting device comprises in particular a dilution valve 23 and acontrol device 60. The dilution valve 23 is disposed between thedilution gas supply line 14 and the respiratory gas supply line 16. Thecontrol device 60 controls the dilution valve 23.

Demand regulator starts supplying first gas mixture (respiratory gas) inresponse to the user of the breathing mask breathing in and stopssupplying respiratory gas when the user stops breathing in.

One can refers to prior art, such as for example to document U.S. Pat.No. 6,789,539 for a more detailed description of a demand regulator. Thepresent invention is also applicable to other types of dilutionadjusting device 24, such as the dilution adjusting device disclosed inpatent application PCT/FR2011/050359 or U.S. Pat. No. 6,789,539 includedby reference.

FIG. 2 schematically represents the flow chamber 30 in whichalternatively flows a first gas mixture flow 32 and a second gas mixtureflow 34. In order to adjust the rate of oxygen to deliver to the user 7,a characteristic (in particular the partial pressure or percentage of agaseous) of a gaseous constituent (in particular oxygen or carbondioxide) of the first gas mixture flow 32 is to be detected by a gassensor 42.

The first gas mixture flow 32 may be either the respiratory gas flow 62or the exhalation gas flow 64, which means that the characteristic ofthe gaseous constituent to sense may be either in the respiratory gas orin the exhalation gas. So, the first gas mixture flow 32 flows from thetubular connecting portion 5 to (the mouth or nose of) the user 7 orfrom the user 7 to the tubular connecting portion 5. Conversely, thesecond gas mixture flow 34 may be either the exhalation gas flow 64 orthe respiratory gas flow 62.

As represented schematically in FIG. 3, between the time 0 and the timeT₁, the gas content in the flow chamber 30 reaches the gas content ofthe first gas mixture flow 32 and then between the time T₁ and the timeT₁+T₂, the first gas mixture flow 32 becomes absent from the flowchamber 30.

As represented schematically in FIG. 4, between the time 0 and the timeT₁, the second gas mixture flow 34 becomes absent from the flow chamber30 and then, between the time T₁ and the time T₁+T₂, the gas content inthe flow chamber 30 reaches the gas content of the second gas mixtureflow 34.

It should be noticed that in FIGS. 3 and 4 the time for filing the flowchamber 30 is neglected.

So, it may be considered by simplification that successively during a T₁period the first gas mixture flow 32 flows in the flow chamber 30 in afirst direction, then during a T₂ period the second gas mixture flow 34flows into the flow chamber 30 in a second direction opposite to thefirst direction, then the first gas mixture flow 32 flows again in theflow chamber 30 during another T₁ period, and so on. The T₁ period maybe considered as equal to the T₂ period, and called T.

The gaseous content of the first gas mixture flow 32 being differentfrom the second gas mixture flow 34, the second gas mixture flow 34disturbs the measurement of the characteristic of the gaseous content ofthe first gas mixture flow 32. It should be understood that the firstgas mixture and the second gas mixture may content the same constituents(at least some identical constituents), and only differ in thepercentage of some of the constituents (in particular percentage ofoxygen, carbon dioxide and steam).

FIG. 5 presents three measurements 42 a, 42 b, 42 c provided by gassensors 42 having different response times Tr for the above describedexample. The measurements 42 a, 42 b, 42 c correspond to gas sensorshaving a response time respectively equal to T/10, T/2 and 2T.

It appears that the gas sensor providing measurements 42 a, 42 b aresuitable for the present example, whereas the gas sensor providingmeasurement 42 c is not appropriate.

So, the shorter the response time of the gas sensor is, the moreaccurate the measurement is. But, a sensor with a short time response isgenerally more expensive than a sensor with a longer time response, andsometimes a sensor with a time response satisfying for a particularapplication does not exist.

FIG. 6 represents a first embodiment of a device 100 in accordance withthe invention. The device 100 is a portion of the breathing mask 4represented in FIG. 1.

The device 100 comprises a flow direction sensor 38, a shutter 50, adriving device 51 and a gas sensor 42 placed in a sensing chamber 40 influid communication with the flow chamber 30 through a passage 66.

The flow direction sensor 38 and the gas sensor 42 are connected to thecontrol device 60. The flow direction sensor 38 detects if the flowdirection in the flow chamber 30 corresponds to the direction of thefirst flow mixture 32. In variant, the flow direction sensor 38 maydetect if the flow direction in the flow chamber 30 corresponds to thedirection of the second flow mixture 34.

The shutter 50 is movable between an active position in which it closesthe passage 66 and an inactive position in which it is away from thepassage 66.

The control device 60 controls the driving device 51 in order to placethe shutter 50 in open position when the flow direction sensor 38detects the first gas flow 32, so that the first gas mixture flow 32(partially) enters in the sensing chamber 40. Moreover, the controldevice 60 controls the driving device 51 in order to place the shutter50 in closed position when the flow direction sensor 38 does not detectthe first gas flow 32, so that the second the second gas mixture flow 34is prevented from entering in the sensing chamber 40.

Therefore, the sensing chamber 40 contains only gas mixture of the firstgas mixture flow 32 at any time. So, the gas sensor 42 transmits adilution signal which accuracy is not influenced by the second gasmixture flow 34. The control device 60 controls the dilution valve 24 inaccordance with the dilution signal generated by the gas sensor 42.

The gas sensor 42 is adapted to determine in particular partial pressure(or percentage) in oxygen (or carbon dioxyde) of the gas contained inthe sensing chamber 40.

The flow direction sensor 38 includes in particular a pressure sensor, apressure gauge sensor, a pressure differential sensor, thermistances, asensor of the state of a check valve or a piezo sensor device comprisinga flexible sheet and detecting the direction of the curvature of theflexible sheet.

FIG. 7 represents a second embodiment of a device 100 in accordance withthe invention.

In this second embodiment, the characteristic of the gaseous constituentto sense is in the respiratory gas, so that the first gas mixture flow32 is the respiratory gas flow 62 and the second gas mixture flow 34 isthe exhalation gas flow 64.

An isolation valve 36 is inserted between the respiratory gas supplyline 16 and the respiratory chamber 9. The gas sensor 42, in connectionwith the control device 60, is placed in the respiratory chamber 16which forms the sensing chamber 40. The isolation valve 36 prevents gasfrom entering into the sensing chamber 16, 40 from the respiratorychamber 9.

In the embodiment illustrated, the isolation valve 36 is a check valve.In variant, it may be an inspiration valve similar to the exhaust valve20.

FIG. 8 represents a third embodiment of a device 100 in accordance withthe invention.

In this third embodiment, the characteristic of the gaseous constituentto sense is in the exhalation gas, so that the first gas mixture flow 32is the exhalation gas flow 64 and the second gas mixture flow 34 is therespiratory gas flow 62.

The isolation valve 36 is inserted between the respiratory chamber 9 andthe exhalation line 18. The gas sensor 42, in connection with thecontrol device 60, is placed in the exhalation line 18 which forms thesensing chamber 40. The isolation valve 36 prevents gas from enteringinto the respiratory chamber 9 from the exhalation line 18.

FIG. 9 represents a fourth embodiment of a device 100 in accordance withthe invention.

The gas detector 42 comprises a pumping plate 44, a first disk of solidionic conductor 45, a common plate 46, a second disk of solid ionicconductor 47 and a sensing plate 48.

The pumping plate 44, the common plate 46 and the sensing plate 48 areelectrodes preferably made of platinum films.

The pumping plate 44, the common plate 46 and the sensing plate 48 areof substantially annular form. Therefore, the sensing chamber 40 isdelimited by the common plate 46, the first ionic conductor 45 and thesecond ionic conductor 47.

A current source 39 is inserted between the pumping plate 44 and thecommon plate 46. The common plate 46 and the sensing plate 48 areconnected to the control device 60, as well as the flow direction sensor38.

The pumping plate 44, the first solid ionic conductor 45 and the commonplate 46 define a pumping electrochemical cell 56. The common plate 46,the second solid ionic conductor 47 and the sensing plate 48 define asensing electrochemical cell 58.

The ionic conductors 45, 47 define solid electrolyte. They arepreferably made in zirconium dioxide suitably adapted for the conductionof ions of oxygen O₂.

The gas sensor 42 further comprises an optional filter 49 surroundingthe pumping electrochemical cell 56 and the sensing electrochemical cell58. The filter 49 prevents particles from entering into the sensor 42.Therefore, the gas sensor 42 includes a buffer chamber 41 extendingbetween the flow chamber 30 and the pumping electrochemical cell 56 (andthe sensing electrochemical cell 58).

The gas sensor 42 may be placed either in the respiratory chamber 9, inthe respiratory gas supply line 16 or in the exhalation line 18, and ofany of the first to third embodiment described above.

As illustrated in FIG. 10, when the electrical power supply 39 outputs apumping current i at the value Ip, oxygen ions are transported throughthe ionic conductors 45 from the sensing chamber 40 to the bufferchamber 41. Therefore, an evacuation phase 28 corresponds to a phase ofpumping current i equal to Ip. So, the partial pressure in Oxygen PO₂ inthe sensing chamber 40 decreases. The voltage Vs between the sensingplate 48 and the common plate, called Nerst voltage, increases.

When the electrical power supply 39 outputs a pumping current i at thevalue −Ip, oxygen ions are transported through the ionic conductor 45from the buffer chamber 41 to the sensing chamber 40. Therefore, apressurisation phase 26 corresponds to a phase of pumping current iequal to −Ip. So, the partial pressure in Oxygen PO₂ in the sensingchamber 40 increases and the Nerst voltage Vs between the sensing plate48 and the common plate 46 decreases.

In operation, the control device 60 causes a repetitive sequence wherethe oxygen pumping current I is successively reversed to maintain theNerst voltage Vs between to predetermined values V₁, V₂.

Therefore, the partial pressure of Oxygen in the sensing chamber 40varies between two values PO₂low and PO₂high.

The period of oscillation Tp is proportional to the oxygen partialpressure in the buffer chamber 41. Therefore, period of the pumpingcycle is used to determine the ambient oxygen partial pressure.

The transportation of the oxygen through the ionic conductor 45 duringthe pressurisation phase 26 creates a pressure drop in the bufferchamber 41. The low porosity of the external filter 49 limits the entryof the ambient gas into the sensor and is responsible of the main delay(high response time) in the oxygen partial pressure measurement.

The response time of the gas sensor 42 generates an error in themeasurement of the oxygen partial pressure in the first gas mixture flow32, due to the second gas mixture flow 34.

As shown in FIG. 11, in order to limit the error in the measurement ofthe oxygen partial pressure in the first gas mixture flow 32, thedirection of the flow in the flow chamber 30 is sensed by the directiongas sensor 38. During step S38, based on the signal provided by the flowdirection sensor 38, the

1. A method for determining a characteristic such as partial pressure orpercentage of a gaseous constituent in a first gas mixture flow in aflow chamber where flows alternatively said first gas mixture flow and asecond gas mixture flow in opposite directions comprising the followingsteps: detecting the occurrence of the first gas mixture flow in theflow chamber, placing a solid ionic conductor of a pump electrochemicalcell interposed between the flow chamber and a sensing chamber, a)pumping said gas constituent from the flow chamber into the sensingchamber through the solid ionic conductor when the occurrence of thefirst gas mixture flow in the flow chamber is detected for introducingthe first gas mixture flow into a sensing chamber when the first gasmixture flow flows in the flow chamber, b) stopping pumping said gasconstituent from the flow chamber into the sensing chamber when theoccurrence of the first gas mixture flow in the flow chamber is notdetected for preventing introduction of gas from the flow chamber intothe sensing chamber at least when the second gas mixture flow flows inthe flow chamber, and c) sensing said characteristic of the first gasmixture flow in the sensing chamber. 2.-10. (canceled)
 11. The methodaccording to claim 1 further comprising pumping said gas constituentfrom the sensing chamber into the flow chamber through the solid ionicconductor during step b).
 12. The method according to claim 1 wherein abuffer chamber is interposed between the flow chamber and the pumpelectrochemical cell, and the buffer chamber communicates with the flowchamber through a filter in (low) porous material.
 13. The methodaccording to claim 1 comprising sensing partial pressure or percentageof a constituent in the first gas mixture flow during step c).
 14. Themethod according to claim 13 comprising sensing partial pressure orpercentage of oxygen in the first gas mixture flow during step c).
 15. Amethod for regulating the rate of oxygen in respiratory gas provided bya breathing mask to an aircraft occupant comprising the following steps:generating the first gas mixture flow by mixing a pressurised breathablegas with a dilution gas, detecting the occurrence of the first gasmixture flow in the flow chamber, placing a solid ionic conductor of apump electrochemical cell interposed between the flow chamber and asensing chamber, a) pumping said gas constituent from the flow chamberinto the sensing chamber through the solid ionic conductor when theoccurrence of the first gas mixture flow in the flow chamber is detectedfor introducing the first gas mixture flow into a sensing chamber whenthe first gas mixture flow flows in the flow chamber, b) stoppingpumping said gas constituent from the flow chamber into the sensingchamber when the occurrence of the first gas mixture flow in the flowchamber is not detected for preventing introduction of gas from the flowchamber into the sensing chamber at least when the second gas mixtureflow flows in the flow chamber, c) sensing said characteristic of thefirst gas mixture flow in the sensing chamber, and adjusting the rate ofdilution gas in the respiratory flow in accordance with thecharacteristic of the first gas mixture flow.
 16. A sensing device fordetermining a characteristic such as partial pressure or percentage of agaseous constituent comprising: a flow chamber, a sensing chamber influid communication with the flow chamber, a gas sensor placed in thesensing chamber and adapted to sense a characteristic such as partialpressure or percentage of a gaseous constituent, a selective deviceisolating the sensing chamber at least when gas flows in a firstdirection in the flow chamber and allowing insertion of gas when gasflows in a second direction opposite to the first direction in the flowchamber, wherein the selective device comprises: a solid ionic conductorof a pump electrochemical cell interposed between the flow chamber andthe sensing chamber, electrical power adapted to alternatively pump agas constituent from the flow chamber into the sensing chamber throughthe solid ionic conductor and from the sensing chamber into the flowchamber through the solid ionic conductor, a control device, a flowdirection sensor connected to the control device and adapted to detect afirst gas flow in a first direction and/or a second gas flow in a seconddirection opposite to the first direction, the control devicecontrolling pumping said gas constituent from the flow chamber into thesensing chamber through the solid ionic conductor when the flowdirection sensor detects the occurrence of the first gas mixture flow inthe flow chamber and for stopping pumping said gas constituent from theflow chamber into the sensing chamber when the flow direction sensordoes not detects the occurrence of the first gas mixture flow in theflow chamber.
 17. A regulator of breathing mask for aircraft occupantcomprising the device according to claim 16 wherein the flow chamber isadapted to provide a respiratory gas to the aircraft occupant and theregulator further comprises: a breathable gas supply line to beconnected to a source of breathable gas and supplying the flow chamberwith breathable gas, a dilution gas supply line to be connected to asource of dilution gas and supplying the flow chamber with dilution gas,a dilution adjusting device adjusting the rate of dilution gas in therespiratory gas supplied to the flow chamber, the dilution adjustingdevice comprising a dilution valve and the control device controllingthe dilution valve in accordance with a dilution signal generated by thegas sensor in function of said characteristic. 18.-22. (canceled) 23.The regulator according to claim 22 wherein a buffer chamber isinterposed between the sensing chamber and the flow chamber, and thebuffer chamber communicates with the flow chamber through a filter in(low) porous material. 24.-25. (canceled)